When a battery supplies energy to the drive system of a hybrid automobile or the like, generally, a voltage of around several hundred V is required; such batteries are often configured by connecting many secondary cells, such as lithium ion batteries, in series. When many secondary cells are connected in series, voltage variations occur because the characteristics of the individual cells are different. During charging, for example, the voltage of some cells may be too high and cause problems, such as damage or fire. For this reason, circuitry is generally provided to sense the voltage of each of the secondary cells connected in series and prevent the occurrence of overvoltages.
In Japanese Kokai Patent Application No. 2001-264,366, a voltage sensing device is described with which the voltage of each module in multiple cell modules that are connected in series is sensed. The voltage sensing device described in FIG. 6 in Japanese Kokai Patent Application No. 2001-264,366, for example, is provided with a multiplexer that selects two nodes from the individual connection nodes of the multiple cell modules connected in series, a differential amplifying type voltage sensing circuit that senses the voltage at the two nodes selected by the multiplexer, and a module voltage correction part that corrects the voltage sensed by the differential amplifying type voltage sensing circuit based on a prescribed correction equation.
With the voltage sensing device described in Japanese Kokai Patent Application No. 2001-264,366, a node of each cell module is first selected by the multiplexer from the multiple cell modules that are connected in series, and the voltage of the selected cell module is sensed by the differential amplifying type voltage sensing circuit. The sensed value is recorded in the module voltage correction part whenever necessary. Then when the sensed voltage values for all the cell modules are acquired, the accurate voltage for each cell module is calculated using the prescribed correction equation.
With the voltage sensing device shown in Japanese Kokai Patent Application No. 2001-264,366, a constant used for correction calculation based on a correction equation in the module voltage correcting part must be acquired before the product is shipped. That is, during pre-shipment inspection, a reference voltage source is connected in place of the cell module and its voltage is sensed, so that the necessary constant is calculated with a prescribed algorithm based on the sensed voltage value obtained. However, this makes pre-shipment inspection time-consuming, and there is also the problem that the same operation is required when a device is to be replaced after shipment. There is also the problem that increased errors due to temporal changes are unavoidable, since the same constant that was acquired at the time of shipment continues to be used.
In addition, with the voltage sensing device shown in Japanese Kokai Patent Application No. 2001-264,366, it is necessary to sense the voltage of all the cell modules in order to obtain the voltage value for each cell module. Because the processing in the module voltage correction part is relatively complicated, in Japanese Kokai Patent Application No. 2001-264,366, it is realized with a microcomputer. Then to acquire an accurate voltage value for each cell module, it is necessary to follow the steps in which each of the sensed values for all the cell modules undergoes analog/digital conversion, the obtained data is transmitted to the microcomputer, and correction calculation is executed based on the data transmitted to the microcomputer. That is, there is the problem that a great amount of time is required until the voltage values are ascertained. When the cell module voltage is monitored to judge abnormalities, such as overvoltages, there is the possibility that such a time delay will become a problem from the standpoint of safety. There is also the problem of increased circuit area and power consumption, since a microcomputer is used.